1. Field of the Invention
This invention relates to an object lens holder employed in an object lens driving controlling device adapted for converging a laser light, radiated from a light source, such as a semiconductor laser, on a signal recording surface of an optical disc, or causing the laser light to follow a recording track(s) on the optical disc. The invention also relates to a method for producing the object lens holder and an object lens holder block comprised of an interconnection of a large number of such object lens holders.
2. Description of the Prior Art
Heretofore, an optical disc player or an optical recording/reproducing apparatus, employing an optical disc as a recording medium, is provided with an optical pickup device for irradiating the signal recording surface of the optical disc with a laser light and detecting the reflected return light from the signal recording surface for recording and/or reading or reproducing information signals on or from the signal recording surface.
The optical pickup device is comprised of a light source, such as a semiconductor laser, radiating the laser light to the signal recording surface of the optical disc, an object lens for converging the laser light radiated from the laser light source to the signal recording surface of the optical disc and a photodetector for detecting the reflected return light from the signal recording surface of the optical disc.
The optical pickup device is provided with an object lens driving device for accurately reading information signals recorded with a high recording density on the optical disc or accurately recording information signals on the recording track(s) of the optical disc. The object lens driving device controls the laser light for accurately converging the laser light radiated from the laser light source on the signal recording surface of the optical disc and causing the laser light to follow the recording track(s) on the optical disc. That is, the object lens driving device actuates the object lens, adapted for radiating the laser light to the signal recording surface of the optical disc, so that the object lens is displaced in a focusing direction or along the optical axis and in a tracking direction normal to the focusing direction, on the basis of focusing controlling signals and tracking controlling signals, so that the laser light is accurately converged on the signal recording surface of the optical disc at the same time that it is caused to correctly follow the recording track(s) of the optical disc.
FIG. 1 shows an example of this type of the object tens driving device, which is of an axial sliding and rotating type device in which a lens holder 152 mounting an object lens 151 is passed through an upright supporting shaft 154 mounted on a supporting base plate 153 so as to be driven along and around the supporting shaft 154. This axial sliding rotating type object lens driving device is so arranged that a focusing driving coil 155 is wound about the peripheral surface of the lens holder 152 and a tracking driving coil 156 is joined to the focusing driving coil 155, while a magnetic circuit made up of magnets 157, 157 and yokes 158, 158 is provided facing the coils 155, 156 on the supporting base plate 153 so as to be operated as an electromagnetic driving unit. Controlling currents conforming to focusing error signals and tracking error signals generated on detection of the reflected return light from the signal recording surface of the optical disc are supplied to the focusing driving coil 155 and the tracking driving coil 156, respectively, for driving and shifting the lens holder 152 along and around the supporting shaft 154. By actuating the lens holder 152 in this manner, the object lens 151, mounted at an offset position relative to the center of rotation of the lens holder 152, is driven and shifted in both the focusing and tracking directions for achieving focusing and tracking control of the optical beam with respect to the optical disc.
FIG. 2 shows another example of an object lens driving device which is of a wire-supported type in which a lens holder 202 mounting an object lens 201 is supported in a cantilever fashion on a supporting base plate 203 by four metal wires 210 having their proximal ends supported by a mounting plate 204 mounted upright on the supporting base plate 203 so that shifting of these wires causes the object lens 201 to be shifted in a direction along the optical axis of the object lens 201 and in a direction normal thereto. With the wire-supported type object lens driving device, a focusing driving coil is wound around the peripheral surface of the lens holder 202 and a tracking controlling coil 206 is joined to the focusing driving coil 205, while a magnetic circuit made up of magnets 207, 207 and yokes 208, 208 is provided facing the coils 205, 206 on the supporting base plate 203 so as to be operated as an electromagnetic driving device. Controlling currents conforming to focusing error signals and tracking error signals generated on detection of the reflected return light from the signal recording surface of the optical disc are supplied to the focusing driving coil 205 and the tracking driving coil 206, respectively, for resiliently biasing the four wires 210 supporting the lens holder 202 for shifting the object lens 201 mounted on the lens holder 202 in a direction along its optical axis and in a direct, ion normal thereto. With the object lens 201 thus shifted, focusing and tracking control of the light beam relative to the optical disc may be achieved.
FIG. 3 shows still another example of the object lens driving device which is of a mold-hinge type in which a lens holder 302 mounting an object lens 301 is supported on a supporting base plate 303 by a supporting arm 304 molded from synthetic resin for supporting the object lens 301 mounted on the lens holder 302 for movement in a direction along the optical axis of the object lens 301 and in a direction normal thereto. The supporting arm 304 of the object lens driving device is formed with first and second hinges 310, 310, 311, 311 extending in a direction along the optical axis of the object lens 301 and in a direction normal thereto. With deflection of the hinges 310, 311 of the supporting arm 304, the object lens 301 mounted on the lens holder 302 is shifted in the above-mentioned two perpendicular directions. The supporting arm 304 has a proximal side supporting block 312 supported by mounting shafts 313, 313 mounted upright on the supporting base plate 303. The lens holder 302 is supported by a lens holder supporting block 315 provided at a distal end of parallel supporting arms 314, 314 extended from the supporting block 312 and supported in this manner on the supporting base plate 303. The first hinges 310, 310, parallel to the optical axis of the object lens 301, are formed on both ends of the parallel supporting arms 314, while the second hinges 311, 311 extending normal to the optical axis of the object lens 301 are formed between the supporting block 312 and the parallel supporting arm 314 and between the lens holder supporting block 315 and the parallel supporting arm 314.
With the above-described molded-hinge type object lens driving device, the electromagnetic driving unit for driving and shifting the object lens 301 in a direction along the optical axis and in a direction normal thereto is made up of a pair of square-shaped focusing driving coils 305, mounted on both sides of the lens holder 302, tracking controlling coils 306 joined to lateral sides of these focusing driving coils 305 and a magnetic circuit comprised of magnets 307, 307 and yokes 308, 308 provided on the supporting base plate 303 for facing the coils 305, 306.
Controlling currents conforming to focusing error signals and tracking error signals generated on detection of the reflected return light from the signal recording surface of the optical disc are supplied to the focusing driving coil 305 and the tracking driving coil 306, as in the case of the above-mentioned first and second examples, for resiliently biasing the first and second hinges 310, 311 of the supporting arm 304 supporting the lens holder 302 for shifting the object lens 301 mounted on the lens holder 302 in a direction along its optical axis and in a direction normal thereto. With the object lens 301 thus shifted, focusing and tracking control of the light beam relative to the optical disc may be achieved.
With the above-described axial sliding and rotating type object lens driving device, shown in FIG. 1, the lens holder 152 is supported for sliding and for being rotated along the supporting shaft 154 and around the supporting shaft by passing the supporting shaft 154 through an engaging hole 152a formed in the lens holder 152 mounting the object lens 151. Thus the lens holder may become unable to be slid and rotated along and around the supporting shaft 154 unless the engaging hole 152a in the lens holder 152 and the supporting shaft 154 are correctly sized relative to each other. If the engaging hole 152 is larger in size than the diameter of the supporting shaft 154, sliding and rotation of the lens holder 152 is accompanied by vibrations. Conversely, if the engaging hole 152 is smaller in size than the diameter of the supporting shaft 154, the sliding load of the lens holder 152 relative to the supporting shaft 154 becomes excessive so that driving cannot be made in conformity to the focusing and tracking control signals. That is, unless the engaging hole 152a in the lens holder 152 and the supporting shaft 154 are correctly sized relative to each other, the lens holder 152 cannot be slid or rotated smoothly along the axis of the supporting shaft 154 or around the supporting shaft 154, so that the object lens 151 cannot be moved smoothly in the direction along the optical axis or in the direction normal thereto and hence focusing and tracking control operations cannot be performed accurately in conformity to the focusing and tracking control signals. The result is that information signals cannot be recorded or reproduced with satisfactory recording/playback characteristics.
Thus the axial sliding and rotating type object lens driving device suffers from the problem that the assembling operation cannot be performed without difficulties.
With the above-described wire-supported type object lens driving device, shown in FIG. 2, in which the lens holder is supported using the above-mentioned metal wires 210, the object lens 201 cannot be shifted accurately in the direction along the optical axis and in the direction normal thereto in accordance with focusing controlling signals and tracking controlling signals, unless the four metal wires 210 supporting the lens holder 202 are mounted between the lens holder 202 and the mounting plate 204 with high parallelism to each other, such that accurate focusing and tracking controlling operations cannot be achieved. The result is that recording and reproduction of the information signals cannot be performed with good recording/playback characteristics.
Thus the wire-supported type object lens driving device also suffers from the problem that the assembling operation cannot be performed without difficulties.
With the above-described molded-hinge type object lens driving device, shown in FIG. 3, in which the lens holder 302 is supported by the supporting arm 304 molded from synthetic resin, it is extremely difficult to mold the supporting arm 304 integrally from synthetic resin. Above all, it is difficult to maintain high machining precision of the hinge part of the supporting arm 304 molded from synthetic resin. Unless the high machining precision of the hinged part is maintained, the object lens 301 cannot be shifted accurately responsive to the focusing and tracking controlling signals in the direction along the optical axis and in the direction normal thereto, such that it becomes impossible to perform accurate focusing and tracking controlling operations. As a result, recording/reproduction of information signals cannot be performed with good recording/reproducing characteristics.
Thus the molded-hinge type object lens driving apparatus suffers from the problem that component parts such as supporting arms can be molded and machined extremely difficultly.